The invention relates to semiconductor technology, and more specifically to plasma applications.
In semiconductor fabrication, various layers of insulating material, semiconductor material and conducting material are formed to produce a multi-level semiconductor device. One of the limiting factors in the continuing evolution toward smaller device size and higher density is resist scum problem.
FIGS. 1A through 1B show how resist scum affects a damascene process.
In FIG. 1A, a substrate 100 comprises an interconnection 110 on a surface. A first etch stop layer 121, a dielectric layer 122, and a second etch stop layer 123 sequentially overlie the substrate 100. Layers 121 through 123 are patterned, forming an opening 125 through layers 121 through 123, exposing the interconnection 110. A resist layer 130 is formed overlying the substrate 100 for patterning the layers 122 and 123 to form a dual damascene structure. A region A indicates a predetermined exposure region in the resist layer 130. When region A is illuminated by an energy ray, photoacids are formed therein to assist development of the resist layer 130.
Unfortunately, the layer 121 is typically formed by chemical vapor deposition (CVD), and alkaline molecules such as ammonia, one of the precursors for the layer 121, may remain in the layer 121 and tend to diffuse therefrom. Conventionally, a degassing process is performed prior to forming the resist layer 130, but rarely completely purges the alkaline molecules from the layer 121. The alkaline molecules still diffuse into the resist layer 130, resulting in neutralization of the photo acids. Neutralization between the alkaline molecules and the photo acids may cause incomplete development of the resist layer 130, leaving scum 131 in a resist opening 135 as shown in FIG. 1B.
Next, the layers 122 and 123 exposed in the resist opening 135 are etched utilizing the patterned resist layer 130 as an etch mask to form a dual damascene opening 126 as shown in FIG. 1C. Scum 131 may also act as etch masks until exhaustion, resulting in formation of ridges 126a where the scum 131 remains.
In FIG. 1D a conductive material is formed to fill the opening 126 as an interconnection 140. The ridges 126a induce high impedance problem in the interconnection 140 due to cross-section reduction of the interconnection 140 in regions B and C, resulting in device failure during electron migration, stress migration, or other reliability testing, negatively affecting device reliability and process cost.